The FBI is investigating whether computer passwords were shared among Hillary Clinton's close aides to determine how sensitive intelligence "jumped the gap" between the classified systems and Clinton's unsecured personal server, according to an intelligence source familiar with the probe.

The source emphasized to Fox News that "if [Clinton] was allowing other people to use her passwords, that is a big problem." The Foreign Service Officers Manual prohibits the sharing of passwords.

Such passwords are required to access each State Department network. This includes the network for highly classified intelligence -- known as SCI or Sensitive Compartmented Information -- and the unclassified system, known as SBU or Sensitive But Unclassified, according to former State Department employees.

Fox News was told there are several potential scenarios for how classified information got onto Clinton’s server...